1. Field of Invention
The present invention relates to a cord lock apparatus for controlling the cords of a window shade, and particularly to a cord lock apparatus which is capable of altering the engaging gap space between the cords.
2. Related Art
Quite frequently, a cord lock apparatus of a window shade operated by a plurality of cords, such as a conventional blind or typically but not necessary a pleated shade, generally is mounted with a locking dog means. For example, U.S. Pat. No. 4,913,210 discloses a cord lock for window shades. FIG. 1 is a front perspective view of a cord lock in the prior art, and FIG. 2 is a sectional side view of FIG. 1. Referring to FIGS. 1 and 2, a base 12 is assembled on either one side of a generally U-shaped top rail 11 of a window shade 10, and at least two or a plurality of cords 13 pass through the base 12 from the lower portion and thence over an engagement mechanism 14. Then, the cords 13 are guided to an exit on top of the base 12, and from there enter the U-shaped top rail 11. Then, the cords 13 exit from the U-shaped top rail 11 to suspend a plurality of shade member 15 and a bottom rail 16. The engagement mechanism 14 uses two stopping members to relatively adjust the gap space therebetween, permitting the cords 13 to pass through. That is, the cords 13 are angularly tilted to a predetermined position, such that the engaging members are relatively forced to rotate to a selective angle, and then the cords are released. Moreover, the cords 13 still are further drawn to an alternative angle, the stopping members are subsequently reoriented by the cords 13 to move to another position so as to lockly engage the cords 13 in place, thereby locking the shade member 15 and the bottom rail 16 to a desirably raised or lowered position.
The way for the engagement mechanism 14 to lock the cords 13 in place is to generate a friction force by alternatively modifying the angle of the stopping members to angularly turn the cords 13 therebetween, and basically the shade member 15 are retained into a fixed position through a “point contact” friction in nature. Therefore, the overall weight of the shade member 15 is completely imposed on this contact point thereon the cords 13, hence the durability of the engaging cords are considerably less in strength. Moreover, though the engagement mechanism 14 can desirably achieve the locking and releasing effect interfering with the cords 13, the gap therebetween the stopping members of the engagement mechanism 14 cannot be adjusted accordingly, so one single specifications of the engagement mechanism 14 can only practically accommodate with limited cords diameters. When the weight or the thickness of the shade member changes substantially, the cords in alternative diameter are required accordingly and the entire engagement mechanism 14 has to be replaced altogether. And thus, the manufacturers must produce engagement mechanisms 14 in a variety of specifications to properly accommodate the varying cords diameters in usage and so that the object of modular design on parts of the window shade cannot be fully achieved. In addition, the consumers or window shade installers must carefully distinguish and select appropriate specifications of the engagement mechanism to prevent inaccuracies in assembly.